The invention pertains to a process of removing dienes from an olefin feedstock. A preferred olefin feedstock is for the production of primary alcohol compositions by skeletal isomerization of the olefins followed by hydroformylation. The olefin feedstock may be purified before and/or after skeletal isomerization. The olefins in the feedstock preferably have a carbon chain length of about 8 to about 36 carbon atoms, preferably about 10 to about 20 carbon atoms, most preferably about 12 to about 18 carbon atoms.
Alcohols of long chain olefins having about 10 to 28 carbon atoms have considerable commercial importance in a variety of applications, including detergents, soaps, surfactants, and freeze point depressants in lubricating oils. These alcohols are produced by a number of commercial processes, such as by oxo or hydroformylation of long chain olefins. Typical commercially available long chain alcohols are the NEODOL(copyright) alcohols available from Shell Chemical Company, the EXXAL(copyright) alcohols available from Exxon Chemical Company, and the LIAL(copyright) alcohols available from Enichem.
In the manufacture of the NEODOL(copyright) alcohols, a redominantly linear olefin feed is subjected to hydroformylation by reacting carbon monoxide and hydrogen onto the olefin in the presence of an oxo catalyst to form an alcohol. Over 80% of the alcohol molecules in the resulting alcohol are linear primary alcohols. Of the branched primary alcohols in the composition, most, if not all of the branching is on the C2 carbon atom relative to the hydroxyl bearing carbon atom. These alcohols subsequently can be converted to anionic or nonionic detergents or general surfactants by sulfonation or ethoxylation of the alcohol, or by conversion of the alcohol to an alcohol-ethoxysulfate.
The NEODOL(copyright) alcohols are commercially successful intermediates to the production of detergents. One reason for this success undoubtedly is that the NEODOL(copyright) alcohols are economically produced with high yields of linear alcohols. The sulfonates of linear alcohols are more biodegradable than the sulfonates of branched long chain alcohols. Since detergents and soaps used by consumers for washing ultimately are released into the environment, the need for surfactants or detergents with maximal biodegradability is well recognized.
The highly linear NEODOL(copyright) alcohols have the advantage of a high level of biodegradability; however, the high degree of linearity of these alcohols also increases their hydrophobicity, thereby decreasing their cold water solubility/detergency. Government regulations call for both increased biodegradability and increased solubility.
Alcohols that have been found to meet both the biodegradability and the solubility government standards are branched primary alcohols (and their sulfate derivatives): having about 8 to about 36 carbon atoms; having an average number of branches per molecular chain of at least 0.7 (defined below); having less than 0.5 atom % of quaternary carbon atoms; and, having at least methyl and ethyl branching. These alcohols, as well as a method for preparing them, are described in U.S. Pat. No. 5,849,960, incorporated herein by reference. The method basically involves contacting a feed comprising linear olefins having 7 to 35 carbon atoms with a skeletal isomerization catalyst, and converting the resulting skeletally isomerized olefin to a saturated branched primary alcohol, preferably by hydroformylation.
Unfortunately, olefin feedstreams have been found to contain at least some level of dienes. Dienes can lower the catalytic performance of many commonly used catalysts, such as those used for skeletal isomerization of olefins and those used for hydroformylation.
The present invention provides a method for purifying an olefin stream comprising: providing an olefin feedstock wherein the olefins have an average molecular chain length of from about 8 to about 32 carbon atoms, the olefin feedstock comprising a first quantity of dienes; and, contacting the olefin feedstock with a hydrogenation catalyst and a gas feed comprising hydrogen at a feedstock flow rate and under conditions effective to reduce the first quantity of dienes to a second quantity of dienes without substantially increasing final paraffin content in the olefin feedstock.
Typical olefin feedstocks comprise from about 100 to about 2000 ppm dienes. The invention pertains to a method for removing these dienes or, more specifically, for selectively converting these dienes to olefins with minimal production of paraffins.
Olefin feedstocks from substantially any source may be treated according to the invention to remove dienes. The invention is not limited to the treatment of olefin feedstocks which are to be subjected to skeletal isomerization and/or to hydroformylation. However, preferred feedstocks are olefin feedstocks which are to be subjected to skeletal isomerization and/or to hydroformylation to produce branched primary alcohols such as those produced in U.S. Pat. No. 5,849,960, incorporated herein by reference. With respect to the process described in that patent, the olefin feedstock may be treated to remove or convert dienes either before or after skeletal isomerization. The method preferably converts about 60 wt. % or more of the dienes to olefins without producing more than about 1 wt. % paraffins.
In order to accomplish the required selective conversion of dienes to olefins, one of the unsaturated carbon-carbon bonds in the dienes is selectively hydrogenated, leaving a monoolefin. The invention accomplishes this selective hydrogenation by feeding the olefin feedstock at a relatively slow (trickle flow) rate to a known, selective hydrogenation catalyst in the presence of a reduced hydrogen content reaction gas.
Any suitable low activity/high selectivity (or xe2x80x9cmildxe2x80x9d) hydrogenation catalyst may be used. Suitable catalysts typically comprise, on a suitable support, a metal selected from Groups 9, 10, or 11 of the Periodic Table of the Elements, F. Cotton et al. Advanced Inorganic Chemistry (Fifth Ed. 1998). Preferred metals for use as a catalytic agent in the present process are Co, Ni, Pd, and Pt, most preferably palladium, either alone or alloyed with Ag, Cu, Co, and combinations thereof. The reactivity of the catalyst may be reduced to achieve selectivity by using less of a more active metal on the support or by using a less reactive metal. Where palladium is used as the catalytic agent, the concentration of palladium on a support is from about 0.05 to about 0.5 wt. %, preferably about 0.05 to about 0.2 wt. %.
Examples of suitable supports for the catalytic metal include, but are not necessarily limited to aluminas, silicas, molecular sieves, activated carbon, aluminosilicate clays, and amorphous silicoaluminas, preferably alumna, silica and carbon. Most preferred support materials are alumina and silica. Preferred supports have up to about 15 m2/g surface area, and preferably have from about 2 to about 5 m2/g surface area. A most preferred catalyst for use in the present invention comprises palladium on an alumina support.
The catalyst may or may not be modified using a suitable promotor, such as chromium, barium, or lanthanium. A preferred promoter is chromium at a preferred concentration of from about 0.05 to about 0.2 wt. %, preferably about 0.05 wt. %. Where chromium is used as a promoter, other suitable additives which may be used at from about 0.05 to 0.25 wt %, preferably about 0.05 wt %, include, but are not necessarily limited to Ba, La, Dy, Ce, Nb, or Sm, preferably Ba or La. A preferred commercially available catalyst is K-8327, a palladium on aluminum catalyst available from W.C. Heraeus GmbH, Catalyst Department PKT, Heraeusstrasse 12-1, D-63450 Hanau, Germany.
Surprisingly, the catalysts preferably are used in a fixed bed trickle flow reaction mode at low feed flow. Persons of ordinary skill in the art would expect that a relatively long exposure time between the feedstock and the catalyst in a trickle flow mode would result in more hydrogenation and an undesirably high production of paraffins in the product. The longer the feedstock is exposed to the catalyst, the more selective the process is to the production of olefins. This is particularly true at a low gas flow and when the level of hydrogen in the reaction gas is limited, preferably to from about 2 to about 6 vol. %, with the remainder being an inert gas, preferably nitrogen. In other words, the longer the exposure to the catalyst and to a reaction gas having a limited hydrogen content, the higher the conversion of dienes, and the lower the yield of paraffins.
The reaction conditions are relatively mild. The olefin feedstock preferably is fed to the fixed bed at about 1 liquid hourly space velocity (LHSV) or less, most preferably about 0.25 to 0.5 LHSV. The reaction pressure may be ambient and is not critical, but preferably is maintained relatively low, from about 20 to about 200 psig, most preferably about 30 psig. The reaction temperature also preferably is relatively low, from about 0xc2x0 C. (32xc2x0 F.) to about 100xc2x0 C. (212xc2x0 F.), preferably from about 26xc2x0 C. (80xc2x0 F.) to about 49xc2x0 C. (120xc2x0 F.), most preferably about 38xc2x0 C. (100.40xc2x0 F.).
Without limiting the invention to any particular mechanism of action, the longer reaction time is believed to give the bulkier, more branched dienes more time to diffuse into the catalyst so that more of the branched dienes are selectively hydrogenated. As to the conversion reaction itself, alpha unsaturated bonds are known to be more reactive than internal unsaturated bonds, particularly when those bonds are conjugated with a second unsaturated bond. Because of this, the non-conjugated dienes are believed to convert to conjugated dienes, and the more reactive, conjugated unsaturated bond is believed to be preferentially hydrogenated.
Olefin feedstocks produced by any number of techniques may be treated according to the present invention. As already stated, the olefins in the feedstock have an average chain length of about 8 to about 36 carbon atoms, preferably at least about 10 to about 20 carbon atoms, most preferably about 12 to about 18 carbon atoms. C8 to C36 olefins have a variety of uses, including but not necessarily limited to uses in paper processing, drilling fluids, and machine or metal working. In a preferred embodiment, the olefin feedstock is either the stream to be skeletally isomerized, or the stream produced by skeletal isomerization in the method for producing the primary alcohols described in U.S. Pat. No. 5,849,960, incorporated herein by reference.
The skeletal isomerization catalyst contains a zeolite having at least one channel with a crystallographic free channel diameter ranging from greater than 4.2 xc3x85 and less than 7 xc3x85., measured at room temperature, with essentially no channel present which has a free channel diameter which is greater than 7 xc3x85. Suitable zeolites are described in detail in U.S. Pat. No. 5,849,960, which has been incorporated herein by reference. Examples of zeolites, including molecular sieves, that can be used in the processes with a channel size between about 0.42 nm and 0.7 nm, include ferrierite, A1PO-31, SAPO-11, SAPO-31, SAPO-41, FU-9, NU-10, NU-23, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-50, ZSM-57, SUZ-4, SUZ-4A, SMO3, DAF-1, MeAPO-11, MeAPO-31, MeAPO-41, MeAPSO-11, MeAPSO-31, and MeAPSO-41, MeAPSO-46, ELAPO-11, ELAPO-31, ELAPO-41, ELAPSO-11, ELAPSO-31, and ELAPSO-41, laumontite, cancrinite, offretite, hydrogen form of stilbite, the magnesium or calcium form of mordenite and partheite.
Particularly preferred zeolites are those having the ferrierite isotypic framework structure (or homeotypic). See the Atlas of Zeolite Structure Types, by W. M. Meier and D. H. Olson, published by Butterworth-Heinemann, third revised edition, 1992, page 98. The prominent structural features of ferrierite found by x-ray crystallography are parallel channels in the alumino-silicate framework which are roughly elliptical in cross-section. Examples of such zeolites having the ferrierite isotypic framework structure include natural and synthetic ferrierite (can be orthorhombic or monoclinic), Sr-D, FU-9 (EP B-55,529), ISI-6 (U.S. Pat. No. 4,578,259), NU-23 (E.P. A-103,981), ZSM-35 (U.S. Pat. No. 4,016,245) and ZSM-38 (U.S. Pat. No. 4,375,573). A preferred skeletal isomerization catalyst for use in conjunction with the present invention is a hydrogen ferrierite catalyst, as described in U.S. Pat. No. 5,510,306, incorporated herein by reference.
Diene removal may occur prior to skeletal isomerization and/or prior to hydroformylation in this procedure. Hydroformylation is a term used in the art to denote the reaction of an olefin with CO and H2 to produce an aldehyde/alcohol which has one more carbon atom then the reactant olefin. Frequently, the term hydroformylation is utilized to cover the aldehyde and the reduction to the alcohol step in total, i.e., hydroformylation refers to the production of alcohols from olefins via carbonylation and an aldehyde reduction process. As used herein, hydroformylation refers to the ultimate production of alcohols.
Illustrative hydroformylation catalysts include, but are not necessarily limited to, cobalt hydrocarbonyl catalysts and metal-phosphine ligands comprising metals including, but not necessarily limited to palladium, cobalt, and rhodium. The choice of catalysts determines the various reaction conditions imposed, including whether diene removal is advisable. Certain catalysts are not as susceptible to diene poisoning as others. In a preferred embodiment, diene removal is used in conjunction with palladium based catalysts, including, but not necessarily limited to palladiumxe2x80x94phosphine ligand catalysts. One of ordinary skill in the art, by referring to any of the well-known literature on oxo alcohols, can readily determine the conditions of temperature and pressure that will be needed to hydroformylate the olefins. An example in addition to U.S. Pat. No. 5,849,960 is EP 0 903 333 A1, incorporated herein by reference.